Postfix setup for remote discourse configuration?


I have setup Postfix with mailgun on seperated VPS for sending mails using this topic;

after finish i still cannot find how or what information i should update the app.yml file for the setting to connect there for sending emails ?

Should i use same username and password and smtp (mailgun smtp ? or my new FQDN smtp mail) with same mailgun and password ? or just comment out the username and password and put my new smtp witch i follow above ?

My idea from this installation with mailgun is that mailgun exposed the server IP and i have setup mailgun with Postfix in seprated server for this reason; so any ddos happen there it wont affect the discourse server;

Waiting any recommendations or support…
Thank you for your time reading my topic.